This invention relates to apparatus for the electrolytic cleaning of wire which is arranged in overlapped, non-concentric loops of about the same diameter.
It is known to clean steel wire in straight-line form by passing it through acid or alkaline electrolyte solutions, while subjecting it to high current densities. Examples of such processes and apparatus therefor are disclosed in U.S. Pat. No. 3,338,809 and U.S. Pat. No. 3,507,767, respectively, both by the same applicant as herein. So far as applicant is aware, it has not been previously suggested to clean wire electrically where the wire is arranged in "Loopro" form.
Initial attempts to electropickle wire arranged in this form were not successful. The outer edges of the loops in the transverse direction consistently had a black, smutty-like appearing residue left on them. Analysis of this residue indicated it was composed of amorphous carbon, believed to be caused by preferential electrolytic attack. From work described in the above-mentioned patents, several factors such as solution temperature, electrode-to-wire spacing, and current density were known to influence preferential attack. However, none of these factors would explain the presence of residue only at the outer edges of the loops.
It is of course known that wire arranged in "Loopro" form contains greater mass at the outer edges of the loops due to its overlapped configuration. Thus, U.S. Pat. No. 3,320,101 McLean, suggests the need for proportionately greater cooling of these areas in a controlled cooling process of wire in "Loopro" form. Therefore, tests were initiated by the applicant to determine what factors may cause less effective cleaning of these outer loop areas.
Tests were carried out on straight wire in a pilot cell, varying several process parameters such as electrolyte temperature, current density, electrode-to-wire spacing, and various electrode configurations. While electrolyte temperature and current density again were confirmed to be significant factors, it was also indicated that electrode width and areas seemed to have an influence on cleaning effectiveness. The tests indicated that low effective electrode-to-wire surface area ratios were undesirable under certain process conditions in that a black residue was left on the wire, similar in appearance to that found in our tests of cleaning wire in the "Loopro" form. This represented a new finding in that the influence of electrode area on leaving residue after cleaning had not been suspected.
Previous work did show that certain minimum effective electrode-to-wire area ratios were necessary to maintain applied voltage requirements at reasonable levels, while still achieving the desired high-current density. Therefore, calculations were made of the electrode-to-wire surface area ratios at intervals across the wire loops. It was indicated that where flat electrodes are used, the ratio varies from 3:1 at the center of the loop to less than 0.67:1 at the outer loop edges. It will be apparent that even if top and bottom flat electrodes were used, a ratio of 3:1 at the outer loop edges could still not be achieved. However, various means were tried for increasing electrode-to-wire surface areas. For example, tests were carried out in the pilot cell using ribbed electrodes, i.e., a flat plate having a central raised rib for increasing electrode area. These tests did not prove successful in eliminating the black residue found on the wire in simulations of conditions similar to processing wire in loop form. While not wishing to be bound by theory, it now appears that it is not mere electrode area which is important, but rather the area of electrolyte between the electrode and wire which is available for conducting current therebetween.
It is therefore the primary object of this invention to provide a system for the electrolytic cleaning of wire, by either acid or alkaline processes, where the wire is arranged in generally horizontal, overlapped, non-concentric loop form.